Thermal simulation of switchgear

In development of low voltage switchgear, proper thermal design becomes more and more important to provide safe function and reliability in spite of miniaturization and increasing performance demanded of modern devices. Due to the high complexity of heat generation and loss processes it is not easy to predict the thermal behavior of devices under various load conditions, i.e., usually numerous tests are required. Rockwell Automation has started thermal simulations of contactors some time ago, and now is working on a three-dimensional (3-D) thermal model of a manual motor controller. This paper describes how to transform well known contact physics into an application oriented thermal simulation. Linking relations of mechanical engineering with contact physics, the influence of the applied tightening torque at the field wiring terminals on the thermal behavior of the device is considered, as well as the modeling of the contact area, taking into account switching arcs during breaking of various load currents. The simulation results are compared with infrared (IR) pictures and thermocouple measurements of existing devices to validate the theory and furthermore reflect its quality.